1. Field of the Invention
The present invention relates to a power train of an automatic transmission, and more particularly, to a power train that realizes eight forward speeds and one reverse speed.
2. Description of Related Art
A typical shift mechanism of an automatic transmission utilizes a combination of a plurality of planetary gear sets. A power train of such an automatic transmission that includes the plurality of planetary gear sets changes rotating speed and torque received from a torque converter of the automatic transmission, and accordingly changes and transmits the changed torque to an output shaft.
It is well known that when a transmission realizes a greater number of shift speeds, speed ratios of the transmission can be more optimally designed and therefore a vehicle can have better fuel mileage and performance. For that reason, an automatic transmission that enables more shift speeds is under constant investigation.
In addition, with the same number of speeds, features of a power train, such as durability, efficiency in power transmission, and size, depend a lot on the layout of combined planetary gear sets. Therefore, designs for a combining structure of a power train are also under constant investigation.
A manual transmission that has too many speeds causes the inconvenience of excessively frequent shifting operations to a driver. Therefore, the positive features of more shift-speeds are more important for automatic transmissions because an automatic transmission automatically controls shifting operations without needing any manual operation.
In addition to various developments regarding four and five speed gear trains, gear trains of automatic transmissions realizing six forward speeds and one reverse speed have been introduced, and also, gear trains realizing more number of speeds are under investigation.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.